Estimated effectiveness of symptom and risk screening to prevent the spread of COVID-19

TLDR

Traveller screening is used to limit COVID‑19 spread, and a prior model examined factors influencing its effectiveness. The study estimates how different screening programs affect COVID‑19 spread using current epidemiological data. The authors model various screening strategies based on known COVID‑19 incubation, symptom onset, and transmission parameters. Even under best‑case assumptions, screening misses more than half of infected individuals, mainly those who are asymptomatic or unaware of exposure, underscoring the need for additional measures and informing evidence‑based policy.

Abstract

Traveller screening is being used to limit further spread of COVID-19 following its recent emergence, and symptom screening has become a ubiquitous tool in the global response. Previously, we developed a mathematical model to understand factors governing the effectiveness of traveller screening to prevent spread of emerging pathogens (Gostic et al., 2015). Here, we estimate the impact of different screening programs given current knowledge of key COVID-19 life history and epidemiological parameters. Even under best-case assumptions, we estimate that screening will miss more than half of infected people. Breaking down the factors leading to screening successes and failures, we find that most cases missed by screening are fundamentally undetectable, because they have not yet developed symptoms and are unaware they were exposed. Our work underscores the need for measures to limit transmission by individuals who become ill after being missed by a screening program. These findings can support evidence-based policy to combat the spread of COVID-19, and prospective planning to mitigate future emerging pathogens.